When you eat a girl out when she is having her period.

Commonly used in text messages or social media as a short form for Very Sound Advice.

(1) The status earned by one who has completed the act of cunnilingus upon a menstruating woman; (2) the status conferred by a menstruating woman upon a sexual partner who has performed cunnilingus upon her; (3) the appearance resembling that of a small bird's wings given by the wearing of menstrual blood upon the lips and face of one who has just completed the performance of cunnilingus upon a menstruating woman, considered to be evidence of having performed a sexual act of an extreme intimate nature.

When you eat a girl out on her period

eating a girl out in her period

To perform oral sex on a female while she is on her period

although it is believed to be involving oral sex it actually refers to the bloody smears on the front of the thighs and groin after having sex with a woman on her period.